Conventional colour photographic silver halide materials are processed by a process which includes a colour development step. When such processing is carried out in a machine it is normal practice to replenish at least the developer to replace components lost in use. Usually the colour developer replenisher is designed to take account of the seasoning effect of halide ions removed from the photographic material during development. This means that when the developer solution is first made up before any processing has taken place a starter solution is also used to introduce sufficient halide so that the initial developer contains the amount of halide ions found in the steady state fully seasoned developer solution.
Redox amplification processes have been described, for example in British Specification Nos. 1,268,126, 1,399,481, 1,403,418 and 1,560,572. In such processes colour materials are developed to produce a silver image (which may contain only small amounts of silver) and then treated with a redox amplifying solution (or developer-amplifier) to form a dye image. The redox amplifying solution contains a reducing agent, for example a colour developing agent, and an oxidising agent which will oxidise the colour developing agent in the presence of the silver image which acts as a catalyst. Oxidised colour developer reacts with a colour coupler (usually contained in the photographic material) to form image dye. The amount of dye formed depends on the time of treatment or the availability of colour coupler rather than the amount of silver in the image as is the case in conventional colour development processes. Examples of suitable oxidising agents include peroxy compounds including hydrogen peroxide, cobalt (III) complexes including cobalt hexammine complexes, and periodares. Mixtures of such compounds can also be used. A particular application of this technology is in the processing of silver chloride colour paper, especially such paper with low silver levels.
Since the amplifying solution contains both an oxidising agent and a reducing agent it is inherently unstable. That is to say, unlike a conventional colour developer solution, developer-amplifier solutions will deteriorate in less than a few hours, often in less than one hour, if left in a sealed container. It will, of course, deteriorate if left in a developing tank. One method of dealing with this problem is to use a discrete amount of processing solution for each unit of photographic material and discard it when the material has been processed. This is the so-called "one shot" approach which generally leads to the maximum chemical usage and effluent generation.
When such an unstable processing solution is used in a processing machine the usual replenishers used for conventional colour developers will not be applicable. In a standard replenishing mode the developer is only replenished while photographic material is actually being processed. This is inadequate for an unstable processing solution because, in addition to a small normal amount of aerial oxidation, the oxidising agent (eg H.sub.2 O.sub.2) will oxidise most of the colour developing agent on standing.
PCT application WO 90/1306 published 1st Nov. 1990 (after the priority date of the present application) which describes a redox amplification system in which oxidant is removed from the developer/amplifier solution after use to increase its stability thus increasing its working life. It will be appreciated that the removal of peroxide from a developer/amplifier bath is a considerable additional task which is preferably to be avoided.